Yeast mutants deficient in sterol and dolichyl phosphate synthesis will be selected on media containing ergosterol, Tween 80, and 2,3-dihydrosolanesol phosphate. These mutants will be blocked before farnesyl pyrophosphate, the branch point for synthesis of sterols and dolichols. Owing to a deficiency in dolichol biosynthesis they will be $ unable to attach oligossacharide units to membrane proteins. The effect of various sterols on cell membrane fluidity will be studied by polarization of fluorescence. The membranes will be isolated from yeast heme auxotrophs grown on sterols which are capable of replacing ergosterol as membrane constituent. The mechanism whereby the methyl groups of lanosterol are oxygenated will be investigated. The role of heme in regulating synthesis of cytochrome apoproteins will be studied.